Tag axle operating system

ABSTRACT

A tag axle operating system comprises a gas circuit with gas at a prescribed pressure and a hydraulic circuit that delivers hydraulic fluid pressure to raise and establish the tag axle in an inactive condition and to lower and establish the tag axle in an active condition. The hydraulic circuit establishes a prescribed hydraulic pressure opposing the gas pressure and a resulting force forcing the tag axle tires to bear against a road surface and the tag axle to accept a predetermined load. A brake valve allows air pressure delivery to operate tag axle air brakes while the prescribed hydraulic pressure is maintained and prevents such delivery to disable the brakes when the prescribed hydraulic pressure is relieved. And the hydraulic circuit operates to relieve the prescribed hydraulic pressure to relieve the force on the tag axle and disable the brakes when the tag axle experiences a predetermined tilt angle.

TECHNICAL FIELD AND RELATED PATENT APPLICATIONS

This invention relates to payload-carrying motor vehicles having a tagaxle and to the following concurrently filed U.S. patent applications:application Ser. No. 12/070,041 entitled “PAYLOAD-CARRYING MOTOR VEHICLEWITH TAG AXLE HAVING PRIMARY AND SECONDARY SUSPENSION”, application Ser.No. 12/070,040 entitled “PAYLOAD-CARRYING MOTOR VEHICLE WITH TAG AXLEHAVING DISABLEABLE BRAKES”, and application Ser. No. 12/070,049 entitled“PAYLOAD-CARRYING MOTOR VEHICLE WITH TAG AXLE HAVE FORCE RELIEVABLESUSPENSION”.

BACKGROUND OF THE INVENTION

Payload-carrying motor vehicles such as dump trucks are limited in theirpayload-carrying ability by various factors including the load capacityof their supporting axles and their related components includingsuspension and tires. Another limiting factor but which is quitedistinct from vehicle component load limitations is governmentregulations. And all these factors impact on the economical use of apayload-carrying motor vehicle in that the more payload the vehicle cancarry, the more profitable the vehicle can be.

With regard to the load limitations imposed by the axles and theirfunctionally related components, a common approach to increasing thepayload capacity has been to add one or more load supporting axles inthe form of auxiliary axles commonly called pusher axles that arelocated between the steer axle and the drive axles; there commonly beingtwo such drive axles employed in the heavy-duty vehicles. And in thecase of pusher axles, it is common practice to suspend them in aretractable manner so that they may be deployed under the command of thevehicle operator as needed to aid in supporting the vehicle.

With regard to government regulations, the Federal Government in respectto bridges in the interstate system establishes weight limits onvehicles using the bridges wherein these limits are based on both thevehicle weight and the vehicle's wheelbase wherein the latter ismeasured as the distance between the center of the vehicle's foremostwheels and the center of the vehicle's rearmost wheels. With the greaterthis wheelbase, the more weight that is allowed under such restrictions.

As a result, a common approach to meeting such restrictions is to add aload bearing auxiliary axle commonly called a tag axle or trailing axlethat is located a remote distance behind the vehicle and operates tosignificantly increase the payload capacity as well as the effectivewheelbase of the vehicle Examples of such in the case of a dump truckare disclosed in U.S. Pat. Nos. 5,823,629; 6,116,698; 6,247,712 and6,189,901. Wherein the tag axle is suspended from the rear end of thetruck's dump body and thereby the truck's frame and on vehicle operatorcommand is conditioned in either a stored inactive condition or anactive condition. And wherein the tag axle is raised to a storedlocation above the rear end of the dump body out of the way of the dumpbody's tail gate in establishing the inactive condition and the tag axleis lowered to a remote location behind the truck frame in establishingthe active condition and a down force is applied to the tag axle forcingthe tag axle tires to bear against a road surface to thereby aid insupporting the truck frame as well as extending the effective wheelbaseof the truck to a significant degree. And wherein the tag axle when inthe active condition adds to the increased load capacity provided byother auxiliary axles commonly referred to as pusher axles that arelocated between the primary axles of the truck.

But in providing such a tag axle, it has been found that there arecertain considerations to address that can enhance the ability of thetag axle and its functionally related components to perform to bestadvantage for the purposes intended. Such as the ability of the tag axleto efficiently support lateral loading on the vehicle frame tending totilt the latter, efficiently accommodate certain varying road conditionsat the tag axle wheels while addressing the effects of maintainingforced loading on the tag axle under certain road and tag axlesuspension and tag axle tire conditions, efficiently addressing theeffects of maintaining forced loading on the tag axle under certain roadand tag axle suspension and tag axle tire conditions, efficientlyaccommodate braking the tag axle wheels while addressing the effect ofsuch braking under certain road and tag axle suspension and tag axletire conditions, and efficiently maintaining both forced loading on thetag axle and tag axle braking while addressing the effects of such undercertain road and tag axle suspension and tag axle tire conditions.

SUMMARY OF THE INVENTION

The present invention in addressing the above areas of considerationresides in providing an operating system for a tag axle having wheelswith tires and air brakes wherein the tag axle is suspended from a motorvehicle and is raised and lowered by pivotal movement about a first axisby operation of parallel-arranged hydraulically-operated actuators andcan also pivot about a second axis located equidistant from the ends ofthe tag axle and laying in a plane at right angles to the first axis.The system comprises a closed gas circuit that is charged with a gas ata prescribed pressure and a hydraulic circuit that is adapted to deliverhydraulic fluid under pressure to the actuators to raise and establishthe tag axle in an active condition and to lower and establish the tagaxle in an active condition.

The hydraulic circuit is adapted when the tag axle is in the activecondition to establish a prescribed hydraulic operating pressureopposing the gas pressure and a resulting force on the tag axle forcingthe tires to bear against a road surface and the tag axle to accept apredetermined load. A brake valve is adapted to allow the delivery ofair under pressure to operate the air brakes while the prescribedhydraulic operating pressure is maintained and to prevent such deliveryto thereby disable the air brakes when the prescribed hydraulic pressureis relieved. And the hydraulic circuit is adapted while the tag axle isin the active condition to relieve the prescribed hydraulic operatingpressure and thereby relieve the force on the tag axle and disable theair brakes when the tag axle experiences a predetermined tilt angle whenpivoting about the second axis.

These and other features and aspects of the invention will become moreapparent from the accompany drawings of exemplary embodiments of thepresent invention and from the description of the exemplary embodimentsthat follows.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a dump truck embodying the present inventionwherein the truck's articulating tag axle is shown in its activecondition;

FIG. 2 is an isometric view of the truck with the tag axle in its activecondition;

FIG. 3 is an enlarged portion of FIG. 2 showing the tag axle and relatedcomponents;

FIG. 4 is an isometric view of the tag axle assembly;

FIG. 5 is an enlarged side view of one of the primary actuators in thetag axle suspension system;

FIG. 6 is a view taken along the lines 6-6 in FIG. 5 when looking in thedirection of the arrows;

FIG. 7 is a plan view of the truck with the cab and truck body removed;

FIG. 8 is a schematic of the truck's air brake system for the servicebrakes;

FIG. 9 is an isometric view of the rear end of the truck;

FIG. 10 is an enlarged view taken along the lines 10-10 in FIG. 9 whenlooking in the direction of the arrows;

FIG. 11 is a side view of the truck dumping a load;

FIG. 12 is a side view of the truck traveling over a crest in a roadwith the tag axle remaining in its active condition;

FIG. 13 is a side view of one of the pusher axle gas springs;

FIG. 14 is a side view of one of the tag axle gas springs;

FIG. 15 is an exploded isometric view of one of the tag axle gas springassemblies;

FIG. 16 is an enlarged side view of the rear portion of the truckshowing the tag axle being raised and wherein certain components havebeen broken away and omitted revealing the tag axle assembly, certaincomponents directly associated with the suspension of the tag axleincluding the toggle linkage, and the far-side tag axle wheel and tire;

FIG. 17 is an enlarged view of a portion of FIG. 16;

FIG. 18 is a view like FIG. 16 but showing the tag axle raised and justprior to the tag axle being toggled into position in its stored inactivecondition;

FIG. 19 is a view like FIG. 18 but showing the tag axle toggled intoposition in its stored inactive condition;

FIG. 20 is an enlarged view of a portion of FIG. 19;

FIG. 21 is a view like FIG. 16 but showing the tag axle being loweredand at an intermediate location where the tag axle has then been toggledinto position for eventual operation;

FIG. 22 is a view like FIG. 21 but enlarged and showing the tag axlefully lowered and in its active condition;

FIG. 23 is a schematic of the electrical circuitry controlling theoperation of the tag axle and the tag axle wheel service brakes;

FIG. 24 is a schematic of the hydraulic fluid/gas circuitry operatingthe tag axle under the control of the electrical circuitry in FIG. 23and wherein the circuitry is shown in establishing the tag axle in itsraised inactive condition and stored location in FIG. 19;

FIG. 25 shows the circuitry in FIG. 24 in establishing the tag axle inits lowered and active condition in FIG. 22;

FIG. 26 shows the circuitry in FIG. 24 in establishing the relief of thedown force on the tag axle while in its lowered condition;

FIG. 27 is an enlarged view of the encircled portion labeled “FIG. 27”in FIG. 3;

FIG. 28 is an enlarged view taken along the lines 28-28 in FIG. 27 whenlooking in the direction of the arrows and with the gas spring omitted;

FIG. 29 is a rear view of the truck with the tag axle in its activecondition and in a normal level attitude and with the coil spring/shockabsorber assemblies for the tag axle wheels omitted;

FIG. 30 is an enlarged view of the encircled portion in FIG. 29 labeled“FIG. 30”;

FIG. 31 is a partial rear view of the truck showing one of the tag axlewheels encountering a depression in a road and the tag axle resultantlytilted and with the coil spring/shock absorber assemblies for the tagaxle wheels omitted;

FIG. 32 is a view like FIG. 28 but of lesser extent and with the tagaxle tilted as shown in FIG. 31;

FIG. 33 is a view like FIG. 31 but showing the same tag axle wheelencountering a deeper road depression and the tag axle resultantlytilted to a greater degree;

FIG. 34 is a view like FIG. 28 but of lesser extent and with the tagaxle tilted as shown in FIG. 33;

FIG. 35 is a partial rear view of the truck showing one of the tag axlegas springs collapsed and the tag axle resultantly tilted and with thecoil spring/shock absorber assemblies for the tag axle wheels omitted;

FIG. 36 is a partial rear view of the truck showing one of the tag axletires deflated and the tag axle resultantly tilted and with the coilspring/shock absorber assemblies for the tag axle wheels omitted; and

FIG. 37 is a side view of another embodiment of a dump truck accordingto the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention is disclosed as embodied in a payload-carryingmotor vehicle in the form of a heavy-duty dump truck 10. Wherein thetruck comprises a forwardly located cab 12 that serves as a vehicleoperator and passenger compartment and a rearward located payloadcontainer 14 commonly referred to as the truck body that is open at thetop and serves to contain a payload such as sand, gravel, dirt andrefuse. And wherein the cab 12 and truck body 14 are mounted on a rigidframe 16 that is supported on a road surface 18 such as pavement or theground by a forwardly located steer axle 20 of the beam type andrearward located tandem drive axles 22 which serve as the truck'sprimary axles and by three auxiliary pusher axles 24 of the beam typewhich are located between the steer axle and drive axles. See FIGS. 1, 2and 7.

The steer axle 20, drive axles 22 and pusher axles 24 are suspendedparallel to each other from laterally spaced locations on the frame 16by suspension systems 26, 28, 30 and have wheels 32, 34, 36 withpneumatic tires 38, 40, 42, respectively. Wherein the steer axle 20 hasa rated load capacity that is significantly greater than that of thepusher axles 24 and to a much lesser extent with respect to that of eachof the drive axles 22 but whose combined rated load capacity issignificantly greater than that of the steer axle. And wherein thepusher axle tires 42 are significantly smaller in diameter than theother wheels and tires.

Both the steer axle suspension system 26 and the drive axle suspensionsystem 28 are leaf spring suspensions of a suitable conventional type.Wherein the drive axle suspension system is of the walking beam typehaving a centrally pivoted beam 43 on each drive wheel side that permitsthe associated foremost drive axle wheels and rearmost drive wheels tomove up and down relative to each other to a significant extent inpassing over bumps and depressions in a road surface. Whereas the pusheraxle suspension systems 30 are gas spring suspension systems of asuitable conventional type having elastomeric bags 44 of uniform wallthickness which serve as gas springs when charged with a suitable gasthat is typically air as in the exemplary embodiment and is suppliedwhen the pusher axles are activated for operation and whose pressure isadjustable to adjust the weight that they support and also to somedegree the weight supported by the steer axle 20 as described below.

The pusher axles 24 are activated by elastomeric bags 45 operativelyassociated with each pusher axle. See FIG. 7. Wherein the elastomericbags 45 are operated by a conventional air pressure supply and controlsystem (not shown) that is under the control of the truck operator andalso serves the gas springs 44 in the pusher axle suspension systems 30.The pusher axles 24 are deployed simultaneously on the supply of airunder pressure to the bags 45 from retracted positions (not shown) wherethese bags are exhausted and the pusher axle tires 42 do not contactwith the road to a position where the pusher axle tires are located asshown for contact with the road. And with the pusher axles 24 thusdeployed, the gas springs 44 in the pusher axle suspension systems arethen supplied with air and at a suitable pressure at each pusher axledetermined by individual pressure regulators (not shown) also under thecontrol of the truck operator. Whereby the pusher axle tires 42 are thenforced as shown to bear against the road surface in support of the truckframe 16 by the thus pressure charged gas springs 44.

The gas springs 44 are arranged with the pusher axles activated and intheir respective suspension systems 30 at their factory recommended meanroad height that is desired for normal bag life. And wherein the gassprings 44 in the exemplary embodiment are charged with an air pressureof about 50-psi that was found compatibly suitable for efficientoperation with the other suspension systems, and can be individuallyadjusted at each pusher axle by the aforementioned pressure regulatorsfor a desired weight distribution and also with respect to the weightcarried by the steer axle 20 to a limited degree. And it will be also beunderstood that by reversing the above-described pusher axle gas springactivation and pusher axle deployment by exhausting the air pressurefrom the gas springs 44 and pusher axle positioning bags 45, the pusheraxles 24 are returned to their retracted locations and the pusher axlegas springs are returned without air pressure to an inactive condition.

The arrangement and geometry of the above axle suspensions support thetruck frame 16 in a desired ride height relationship that issubstantially parallel to the road surface as shown in FIG. 1 when thetruck body is loaded and unloaded. And wherein the truck is establishedwith a roll axis 46 as shown in FIG. 2 and with respect to which theframe 16 can pitch and roll under control by the above axle suspensionsand can also possibly yaw but to a very limited degree when the truck isturning at a high speed on a curved road.

The steer axle 20 is located forward of the cab 12 and its wheels 32 aremounted in a conventional manner on pivotal spindles (not shown) on theends of the steer axle 20 and are steered from the cab by the vehicleoperator acting through a tie rod and steering gear arrangement (notshown) of a suitable conventional type. The tandem drive axles 22 eachinclude differential gear-driven axle shafts 47, are located beneath arear portion of the truck body 14, and have dual wheels 34 that areconnected to the outboard end of the respective axle shafts. See FIG. 7.The four drive axle wheels 34 are driven with power received from apower train 48 of a suitable conventional type having an engine 50located forward of the cab 12 and together with a transmission 52 iscontrolled from the cab by the vehicle operator to deliver power to thedrive axle wheels. And wherein fuel is supplied to the engine 50 by fueltanks 54 that are mounted on the truck frame 16 in locations atopposites sides of and below the cab and frame. And mud flaps 55 areprovided that are hung from the lower rear end of the truck body 14 tohang behind the rearmost drive axle tires 40.

The steer axle wheels 32, drive axle wheels 34 and pusher axle wheels 36have air-operated service brakes 56, 58, 60 of a suitable conventionaltype, which are also referred to herein as simply air brakes and includewhat are commonly referred to as air pots 62, 64, 66, respectively, thatserve the brake actuators (not shown) in applying braking force to theassociated wheels. See FIGS. 7 and 8. And wherein the service brakes andair pots are part of an air brake system that further includes an aircompressor 68 that is driven by the engine 50 and supplies air underpressure via a tank supply line 70 to an air tank system comprising aprimary air tank 72 and three secondary air tanks 74 that serve as airpressure accumulators and are spaced along and mounted on anintermediate longitudinal portion of the frame. And wherein thesecondary air tanks 74 are interconnected by separate air lines 76 and77 and are connected to the primary tank 72 by an air line 78 connectingthe closest secondary air tank and thus the other secondary air tanks tothe primary air tank 72.

The air tank system further includes a pressure regulator (not shown)that regulates the pressure in the tank system to a suitable constantpressure for brake operation. Wherein the primary air tank 72 isconnected by an air pressure supply line 80 to deliver the air atconstant pressure to a foot-operated foot valve 82 of a suitableconventional type and by air pressure supply lines 84 to five likepilot-operated quick-release valves 86 that are also of a suitableconventional type.

The foot valve 82 is operated by the vehicle operator from the cab andwhen so operated supplies air at constant pressure from the air tanksystem via the brake supply 80 and an air brake line 88 and branch brakelines 90 directly to the steer axle brake air pots 62 to operate thesteer axle service brakes 56 and via pilot pressure air lines 92 to thequick release valves 86 that are thereby conditioned to deliver the airat constant pressure from the air tank system via the associated supplylines 84 and thence separate and associated branch brake lines 94 to thedrive axle brake air pots 64 and the pusher axle brake air pots 66 tooperate the associated drive and pusher axle service brakes 58 and 60,respectively.

Continuing on with the other truck components, the truck body 14 is openat the top for receiving a load such as dirt, sand and gravel and isalso open at the rear thereof. And wherein structural-reinforcingdouble-wall side panels 96 comprise and define the lateral extremitiesof the truck body at the open rear end thereof where an outwardlyswinging tail gate 98 is hinged in a conventional manner to the upperend of the side panels. And it will be understood that upon the truckbody receiving a load that is captured by the tail gate, the center ofgravity of the truck has shifted upward to a significant degree and isthen what is commonly called top heavy and more prone to rolling aboutthe roll axis 46 in response to lateral loading on the truck frame whenthe vehicle is turning. Wherein the lateral loading increases withincreasing vehicle speed and decreasing turn radius.

The truck body 14 is hinged in a conventional manner at the lower end ofthe side panels 96 to the truck frame 16 and is operated by a tilt bodyactuator 100. See FIG. 11. Wherein the actuator 100 is ahydraulically-operated multistage actuator of a suitable conventionaltype and is operatively connected between the frame 16 and the front endof the truck body 14 in a conventional pivotal manner. Whereby the truckbody 14 can be tilted by operation of the actuator 100 from a nestingposition on the truck frame 16 as shown in FIG. 1 to a steep-angleddumping position or attitude as shown in FIG. 11. A hydraulic circuit(not shown) of a suitable conventional type provides for operation ofthe truck body tilt actuator 100 and includes remote manual controlswhereby the vehicle operator can operate the truck body tilt actuator100 from within the cab and also while along side the truck. And withthe pusher axles 24 normally retracted during backing up of the truckand then dumping of a load as shown in FIG. 11.

The tailgate 98 is latched and held in a closed position as shown inFIGS. 2, 9 and 10 by a manually operated latching mechanism 102 of aconventional type of which only a portion is shown in FIG. 10 andincludes twin, hook-type latches 104 that engage a lower edge portion ofthe tailgate to hold the tailgate in its closed position to prepare thetruck body to receive a load. This holding condition of the latches 104being shown in solid line in FIGS. 2 and 9 and in phantom line in FIG.10. The truck body 14 after receiving a load and delivery to a drop siteis then tilted by the truck body tilt actuator 100 with the latches 104disengaged from the tailgate 98 as shown in solid line in FIG. 10 byoperation of the latching mechanism 102. Whereupon the tailgate isforced to swing outwardly in the opening direction by the force ofgravity and the force of the load acting thereon as the load is beingdumped as shown in FIG. 11.

A tag axle 106, that is also referred to as a trailing auxiliary axle,is of the centrally pivoted beam type and is suspended from the rear endof the truck frame 16 in an articulating manner by a tag axle suspensionsystem 108 to thereby become an integral operational part of the truck.Wherein the tag axle 106 has wheels 110 with pneumatic tires 112 andservice brakes 114 as seen in FIG. 3 and the track width of the tag axlewheels as seen in FIG. 7 is substantially the same as that of theinboard wheels 34 of the drive axles 22 and allows location of the tagaxle with its wheels above the end of the truck body withoutinterference by the latter when the tag axle is moved into this locationas described later.

The tag axle wheels 110 are self-steering in that they are steered bytruck motion as the truck is turned by the truck operator steering thesteer axle wheels 32 and are rotatably mounted on spindles 116 that arepivotally connected with king pins 118 at a suitable camber and casterangle to the tag axle 106 next to the tag axle wheels and areinterconnected by an adjustable tie rod 120. See FIGS. 3 and 4. Whereinthe tie rod 120 is pivotally connected at its ends to one end of steerarms 122 that are rigidly joined at their other end to the tag axlewheel spindles 116. And wherein the tie rod 120 is adjusted lengthwiseto provide the tag axle wheels with a suitable toe-in and the steerabletag axle wheels are stabilized and returned following their forcedsteerage to a normal neutral condition by two like coil spring/shockabsorber assemblies 123 that are connected between the steer arms 122and the tax axle assembly as described in more detail later. And withthe tag axle wheels 110 being steerable, trailing fenders 124 having atail light/brake light are provided for these wheels and are mountedwith an arm 125 on the respective tag axle wheel spindles 116 to trailbehind and thus turn conjointly with the respective tag axle wheels whenthe tag axle is in its active condition.

The tag axle service brakes 114 are conventional type air brakes likethe other service brakes and include air pots 126 that are mounted onbrake actuator assemblies 127 that are located on the inboard end of thewheel spindles 116 as shown in FIG. 4. And the air pots 126 areconnected by a brake line 128 and branch brake lines 130 to receive airat a constant or regulated pressure for operation from the air tanksystem via the rear-most quick-release valve 86 serving the rear-mostdrive axle brakes 58, and a solenoid valve 132 that serves to enable anddisable the tag axle brakes 114 by controlling air pressure supplythereto. See FIG. 8.

The solenoid valve 132 is normally closed when without power andreceives power to open and thereby allow air pressure supply to the tagaxle service brakes 114 to assist in braking the truck when the tag axleis in its active condition with the tag axle forced downward to assistin supporting the truck frame 16. But when the down force on the tagaxle is relieved while the tag axle remains lowered under certaincircumstances as described in detail later, power to the solenoid valve132 is interrupted causing it to close and thereby disable the tag axleservice brakes as also described in detail later.

Describing now the tag axle suspension system 108, it includes both aprimary suspension arrangement and a secondary suspension arrangementand comprises parallel arranged suspension arms 134 that are pivotallyconnected at one end by a pivot pin 136 to a lower end portion of one ofthe truck body side panels 96 and thus in structurally reinforced mannerto the rear end of the truck frame 16 through the hinged end of thetruck body. And a hollow crossbeam 138 that extends parallel to theaxles 20, 22, 24 rigidly connects the suspension arms 134 together attheir other end across the width of the truck body. The pivot pins 136are axially aligned and support the suspension arms 134 and crossbeam138 for swinging movement about an axis extending transversely of thetruck frame parallel to the axles 20, 22, and 24 and thus in a pitchingdirection with respect to the roll axis 46.

The tag axle 106 is linked to the crossbeam 138 and thereby to the outerend of the suspension arms 134 by suspension arms 140 that areconsiderably shorter than the suspension arms 134, are pivotallyconnected at one end by a pivot pin 142 to a tag axle anchoring bracket144 that is welded to the crossbeam 138, and are welded at their otherend to a tag axle carriage 146 to form an integral portion thereof. SeeFIGS. 1-3 and 17. The pivot pins 142 thus connecting the inner end ofthe short suspension arms 140 to the outer end of the long suspensionarms 134 are axially aligned and provide a pivot axis for the shortsuspension arms 140 parallel to that of the significantly longersuspension arms.

A trunnion body 148 is welded to the tag axle 106 at a central locationon the tag axle and is received in a sandwiching manner by opposingsides of the carriage 146. And the tag axle 106 is pivotally connectedequidistant from its ends to the tag axle carriage 146 by a pivot pin150 that extends through axially aligned cylindrical collars 151 on thesandwiching sides of the tag axle carriage and through axially alignedcylindrical collars 152 on the intermediately located tag axle trunnionbody 148. See FIGS. 4 and 28. Wherein the pivot pin 150 is located bythe collars 152 at a location offset from the centerline of the tag axle106 and together with the trunnion body 148 form a tag axle trunnionmounting the tag axle 106 on the carriage 146 for pivotal or tilting tagaxle motion at a location equidistant from the ends of the tag axle andin a plane at substantially right angles to the roll axis 46 when thetruck is on a level surface and the tag axle is in its active conditionas described later.

The trunnion body 148 is further utilized in connection with the tagaxle 106 when the latter is deployed in that the steerable tag axlewheels 110 are stabilized in a non-steering condition and returned tothis condition following their forced steerage with turning of the truckby the coil spring/shock absorber assemblies 123 that are connectedbetween the steer arms 122 and the trunnion body 148 and also serve tomaintain the tag axle wheels in their non-steering condition while thetag axle is raised and lowered. Wherein the coil spring/shock absorberassemblies 123 are mounted for these purposes at their shock absorberpiston rod end in a sleeved elastomeric bushing (not shown) in acylindrical pocket 154 in the respective steer arms midway thereof andare pivotally connected at the closed end of their shock absorber by apivotal joint 156 to an arm 157 fixed to the trunnion body 148 at alocation that is outboard of and below the tag axle pivot pin 150. SeeFIGS. 3 and 4.

The centerline of the tag axle pivot pin 150 is located equidistant fromthe tag axle wheels 110 and lays in a plane at right angles to the pivotaxis of the long suspension arms 134 and is located above the centerlineof the tag axle 106 when the truck is on a level surface and the tagaxle is in its active condition. And the tag axle 106 while in itsactive condition is thereby suspended from the truck frame 16 via thetruck body 14 parallel to the other axles for swinging or pivotalmovement about a first axis extending parallel to the steer, drive andpusher axles established by the long suspension arm pivot pins 134 andalso for tilting or swinging about a second axis established by the tagaxle pivot pin 150 which is thus located equidistant from the tag axlewheels and lays in a plane at right angles to the aforementioned firstaxis.

The tag axle suspension system 108 further comprises twoparallel-arranged primary actuators 158 and a secondary actuator 160that is also referred to herein as a toggle cylinder and operates inseries relationship with the primary actuators in the tag axlesuspension system. See FIG. 17.The primary actuators 158 and the togglecylinder 160 provide separate functions in forming together with thelong suspension arms 134 and short suspension arms 140 the primary tagaxle suspension in the tag axle suspension system 108 for the tag axle106 wherein the toggle cylinder operates through toggle linkage 161 toposition and hold the tag axle carriage 146 and thereby the tag axle 106in certain spatial relationships with respect to the long suspensionarms 134 when the tag axle is raised and lowered as described in detaillater. Whereas the primary actuators 158 incorporate a gas spring andoperate in the primary tag axle suspension to raise and lower the tagaxle and force the tag axle when lowered to accept a predetermined loadwhile providing hydraulically forced gas spring action accommodatinglarge up and down movement of the tag axle as described in detail later.

The primary actuators 158 are located on opposite sides of the truckbody, extend along the upper side of the long suspension arms 134 andare connected between the outer end of these arms and the rear end ofthe truck frame 16 via the lower end of the truck body side panels 96.Referring to FIGS. 5 and 6, the primary actuators 158 comprise acylinder 162 that is closed at one end and has a bore 164 receiving adouble-faced piston 166 that is acted on at both faces by hydraulicpressure and is hereinafter also referred to as a hydraulic piston. Thepiston 166 has a central opening 168 extending there through and isrigidly secured to one end of a hollow piston rod 170 that extendsoutward from the cylinder 162 and terminates with a closed outer end.The piston rod 170 has a bore 172 extending inwardly from the centralopening 168 in the piston 166 receiving a rod-less double-faced piston174 that is acted on by both hydraulic pressure and gas pressure and ishereinafter also referred to as an accumulator piston to distinguish itfrom the hydraulic piston 166 and in a functionally related manner. Andwherein the accumulator piston 174 is captured in the piston rod bore172 by the piston 166 whose central opening 168 for that purpose issmaller in diameter than that of the accumulator piston.

The cylinders 162 of the primary actuators 158 are pivotally connectedat their closed end by axially aligned pivot pins 176 to a lower endportion of the truck body side panels 96 at locations above the longsuspension arm pivot pins 136 and thus like these arms in a structurallyreinforced manner to the rear end of the truck frame 16 by the hingedend of the truck body. And the hollow piston rods 170 of the primaryactuators 158 which also provide cylinders for the respectiveaccumulator pistons 174 are pivotally connected at their closed end byaxially aligned pivot pins 178 to the outer ends of the long suspensionarms 134 and thus to the tag axle carriage 146 via the crossbeam 138.

The closed end of the primary cylinders 162 cooperates with one annularface of the associated piston 166, cylinder bore 164, one end face ofthe accumulator piston 174 and the rod bore 172 to define a hydraulicchamber 180 at this end of the cylinder which is accessed by a hydraulicline fitting 181. The other end of the primary cylinders 162 has adetachable collar 182 that cooperates with the associated cylinder bore164 and the other slightly smaller annular face of the piston 166 todefine a hydraulic chamber 184 at this end of the cylinder 162, which isaccessed by a hydraulic line fitting assembly 185. While the closed endof the piston rods 170 cooperates with the other end face of therespective accumulator piston 174 and rod bore 172 to define a variablevolume gas chamber 186 at this end of the primary actuators 158 which isaccessed by a port 187.

A cylindrical tank 188 that serves as a gas pressure accumulator and alarge extension of the expansible gas chamber 186 in the primaryactuators 158 is mounted in the hollow crossbeam 138 and is connected atopposite ends by flexible hoses 190 to the respective gas chambers. SeeFIGS. 2 and 3. The gas accumulator 188 is of a size that substantiallyfills the crossbeam 138 in maximizing the gas volume available andtogether with the connected hoses 190 and the variable volume gaschamber 186 in each of the primary actuators 158 form a closed gascircuit. That is charged with a suitable gas free of water vapor and ata suitable pressure to thereby form with the variable volume gas chamberin each primary actuator a gas spring that acts on the tag axle. In theexemplary embodiment, this gas is nitrogen and its charge pressure isabout 85-87 percent of a certain operating hydraulic pressure in the tagaxle operating system when the tag axle is lowered and established inits active condition as described in more detail later.

The toggle cylinder 160 operates through the toggle linkage 161 toposition and hold the tag axle 106 in two fixed positions with respectto the long suspension arms 134 and is located intermediate the shortsuspension arms 140 and connected by the toggle linkage 161 between thetag axle anchoring bracket 144 and the tag axle carriage 146. Andwherein the toggle cylinder 160 is of a conventionalhydraulically-operated type comprising a hydraulic cylinder 192 that isclosed at one end and a piston 194 that is received in the cylinder 192and has a piston rod 196 extending outward thereof. See FIGS. 17, 20 and24-26.

As shown in FIGS. 3 and 17, the closed end of the hydraulic cylinder 192is pivotally connected to the short suspension arms 140 at a locationnear the tag axle carriage 146 by a pivot pin 198 and the outer end ofthe piston rod 196 is pivotally connected by a pivot pin 200 to one endof a toggle arm 202 that is also pivotally connected at this end by apivot pin 204 to one end of a toggle link 206 that is short as comparedto the toggle arm and together therewith comprise the toggle linkage161. The other end of the toggle arm 202 is pivotally connected by apivot pin 208 to the tag axle carriage 146 and the other end of thetoggle link 206 is pivotally connected by a pivot pin 210 to the tagaxle anchoring bracket 144 at a location laterally spaced from the shortsuspension arm pivot pins 142.

The pivotal arrangement of the arm 202 and link 206 in the togglelinkage 161 is such that with the piston rod 196 extended to the maximumextent possible by its piston 194 in the hydraulic cylinder 192, thecenterline of the pivot pin 204 is located slightly to one side of aplane passing through the centerlines of pivot pins 208 and in thedirection away from the toggle cylinder 160 and thereby establishing thetoggle linkage in an over-center locked condition. See FIGS. 16, 17, 18,21 and 22. Whereby when the tag axle tires 112 are forced against theroad surface with the toggle linkage 161 in its over-center lockedcondition as shown in FIG. 22, the reaction force on the tag axle 106acts to pull on the already fully extended piston rod 196. As a result,the more locked the toggle linkage 161 becomes in holding the tag axledown with the toggle cylinder 160 with the force being applied on thetag axle 106 by the primary actuators 158. And the toggle cylinder 160being of a conventional type has hydraulic chambers 212 and 214 atopposite sides of the piston 194 (see FIGS. 24-26) for receivinghydraulic fluid under pressure to respectively extend and retract thepiston rod 146 and toggle the tag axle 106 as described in detail later.

The primary actuators 158 and the secondary actuator or toggle cylinder160 are operable to position the tag axle 106 in a stored inactivecondition in a location above the rear end of the truck body out of theway of the tail gate as shown in FIGS. 9, 19 and 20 and in a deployedactive condition at a remote trailing location where the tag axle trailsbehind the truck frame and drive axles as shown in FIG. 22. And in theexemplary embodiment, this trailing distance is for example set at 10-12feet in the setup of the tag axle suspension system geometry dependingon the intended truck usage and thereby increases the effectivewheelbase of the truck to a very significant degree. And wherein acertain operating or working hydraulic pressure together with gaspressure in the tag axle operating system operate to apply a prescribeddown force on the tag axle forcing the tag axle tires to bear against aroad surface thereby forcing the tag axle to accept a prescribed loadwith gas spring action to aid in supporting the truck fire and theexisting weight or load thereon together with the other axles and theirtires.

Such operation is described in more detail later but it is to beunderstood at this point that the tag axle 106 while in its activecondition is suspended from the truck frame 16 by the tag axlesuspension system 108 in a manner wherein the tag axle is linked by thesuspension arms 134 and 140 to move laterally conjointly with the truckframe 16. And wherein the primary actuators 158 together with thesuspension arms 134 and 140 and in forming the primary tag axlesuspension in the tag axle suspension system 108 allows and controlssubstantial pitching motion of the tag axle 106 and thus up and downmovement of the tag axle wheels 110 in relation to the truck frame 16and roll axis 46 in maintaining the tag axle tires 112 in load bearingcontact with the road when passing over bumps and dips and holes in theroad. And also after the steer, drive and pusher axles of the truckfirst pass over a considerable or extreme but brief change in elevationsuch as can occur in passing over a high crest in the road at a railroadcrossing as shown in FIG. 12. And wherein the primary tag axlesuspension with the primary actuators 158 and the centrally pivoted tagaxle 106 helps support the down force on the truck frame 16 togetherwith the other axles except for lateral loading on the truck frame byreason of the tag axle mounting.

The secondary tag axle suspension in the tag axle suspension system 108operates in a secondary manner with respect to the primary tag axlesuspension and comprises the tag axle 106 as pivotally mounted on thecarriage 146 and gas springs 216 of elastomeric bag construction likethe pusher axle gas springs 44 which are located on opposite sides ofthe pivot pin 150 and operatively connected between the tag axle and thecarriage 146 that constitutes the end of the primary tag axlesuspension. See FIGS. 3 and 29. The gas springs 216 are continuouslyfilled with air under pressure unlike the pusher axle gas springs 44 andeach have an integral base plate 217 that is fixed to a lower mountingbracket 218 with bolts 218A and an integral top plate 219 that fixed toan upper mounting bracket 220 with bolts 220A. See FIGS. 14 and 15.

The gas springs 216 are mounted in the secondary tag axle suspension ina strategic manner at locations in close proximity to the tag axle pivotpin 150 intermediate the latter and the tag axle wheels 110 with theirlower bracket 218 welded to the upper side of the tag axle 106 and theirupper mounting bracket 220 welded to an outer side of the tag axlecarriage 146 that faces the respective gas spring 216. Whereby the tagaxle gas springs 216 are arranged in the secondary tag axle suspensionso as to accept and accommodate only the lateral loads or forces on thetruck frame acting to tilt the frame. While the primary actuators 158acting through the long suspension arms 134 in the primary tag axlesuspension accept and accommodate the loads or forces on the truck frameacting downward on the truck frame but not to tilt the frame as well asallowing very significant up and down movement of the tag axle becauseof differences in road elevation between the tag axle and the otheraxles.

The tag axle gas springs 216 have an air charge nipple 216A that is likea Schrader valve and are charged via their nipple with air at a pressureof about 100-psi or twice that of the pusher axle gas springs 44 andalso unlike the pusher axle gas springs remain charged. And with the tagaxle 106 deployed and in its active condition, the tag axle gas springs216 like the pusher axle gas springs 44 are arranged at their factoryrecommended mean road height that is desired for normal bag life. Andalso unlike the pusher axle gas springs 44, the tag axle gas springs 216in addition to having a significantly higher air pressure also have asignificantly smaller spring compliance or stroke than the pusher axlegas springs and thereby contribute significantly in stabilizing thetruck frame under lateral loading. Wherein the gas springs 216 only needa relatively small stroke because of their close proximity to the tagaxle pivot pin 150 and thereby have the ability to allow proportionallygreater tag axle wheel amplitudes but not to the extent of that allowedof the pusher axle wheels by their gas springs 44. And the secondary tagaxle suspension with the pivotal tag axle 106 and gas springs 216 thuscontributes to a significant degree in supporting lateral loading on thetruck frame and with the ability to also efficiently accommodate bumpsand depressions to a satisfactory degree while also preventingtransmittal of shock loads at the tag axle wheels back to the truckframe such as occurs when one of the tag axle tires encounters apothole.

In comparing the characteristics of the tag axle gas springs 216 andtheir mounting to the spring characteristics and arrangement of theother axle suspension systems which contribute to the enhanced use ofthe tag axle 106, the pusher axle gas springs 44 have three annularelastomeric wall sections 221 of exterior convex shape (see FIG. 13) andabout a 13.5-inches spring compliance or stroke in order to accommodateup and down movement of the pusher axle wheels 36 relative to the truckframe to a desired degree as the truck passes over bumps and dips andholes in a road surface while continuing to support the truck frame.Wherein the pusher axle gas springs 44 as arranged in their suspensionssystems on the truck allow upward pusher axle wheel movement relative tothe truck frame up to about 8.5-inches as determined by suitablyarranged bump stops (not shown) to accommodate bumps in a road up tosuch height and allow maximum downward pusher axle wheel movementrelative to the truck frame of about 3.75-inches to accommodate roaddepressions to that depth and still continue to support the truck frame.The total allowed up and down movement of the pusher axle wheels 36 isthus 12.25-inches and the significant difference between the allowedupward movement and allowed downward movement of the pusher axle wheelsis typical and allows the pusher axle gas springs 44 to accommodate roadbumps of considerable height but road dips or depressions to asignificantly lesser degree. And where the depth of the road depressionsuch as a dip or pothole does exceed the limit of downward movementallowed of the pusher axle wheels by their gas springs 44, the pusheraxle tires 42 loose road contact and the pusher axles 24 are thenwithout weight acting thereon and no longer support the truck frame andcan not perform their intended function.

In further contrast with the pusher axle gas springs 44, the tag axlegas springs 216 have only a single annular elastomeric wall section 222of exterior convex shape (see FIGS. 14 and 15) and about a 3.7-inchesspring compliance or stroke that is thus about 27% (3.7/12.25) that ofthe pusher axle gas springs 44 and which by their arrangement withrespect to the tag axle 106 and tilting about the tag axle pivot pin 150allow up and down movement of the tag axle wheels 110 relative to thetruck frame that is the same in both the up and down directions. Whereinthe tag axle gas springs 216 on tilting of the tag axle when the tagaxle wheels encounter bumps and depressions and potholes and alsolateral or asymmetric loading on the truck frame will allow depending onwhich tag axle wheel 110 is affected either upward or downward movementof this wheel of about 2.3-inches corresponding to a tag axle tilt angleof 3.5-degrees before the tag axle is relieved of pressured down forceand no longer helps to support the truck frame as described later. Andwherein it will be understood that this allowed upward and downwardmovement of 2.3-inches is thus the allowed amplitude of the tag axlewheels 110 before the pressured down force is relieved.

However, it will also be appreciated that the tag axle gas springs 216are capable of accommodating considerably more amplitude of the tag axlewheels if the tag axle was not relieved of pressured down force at the3.5-degree tilt angle. For example, the gas springs 216 in the exemplaryembodiment have a factory rated burst pressure of 300-psi and arecharged at 100-psi. And if the pressured down force is not relieved onthe tag axle at 3.5-degrees tilt angle as described later, one of thetag axle wheels 110 on encountering a bump about 3.3-inches high or adepression or hole about 3.3-inches deep would cause a tilt angle of5.0-degrees that can be accommodated by the available stroke of the tagaxle gas springs 216 and wherein the pressure in the tag axle gas springthen being compressed would rise to a pressure only less than half ofthe rated burst pressure of the gas springs. And with the pressured downforce on the tag axle not relieved and should one of the tag axle wheelsencounter an even higher bump such as about 4.6-inches high or a deeperdepression or hole about 4.6-inches deep resulting in a tag axle tiltangle of 7.0-degrees and an companying rise in pressure in the tag axlegas spring being compressed, the tag axle gas springs 216 canaccommodate this situation as well. As this is still within theavailable stroke of the gas springs and the increase in pressure isstill far below their rated burst pressure of 300-psi.

And it will be noted at this point that the total allowed up and downmovement of the tag axle wheels that can occur with the tag axle gassprings 216 is about 4.6-inches while the tag axle is pressured down andis significantly less than that allowed of the pusher axle wheels 36 andin the exemplary embodiment is thus about 38% (4.6/12.25) that of thepusher axle wheels. And this is compensated for by the primary tag axlesuspension wherein the primary actuators 158 accommodate significantlymore up and down tag axle wheel movement than that capable of the pusheraxle wheels 36 even with the pusher axle gas springs 44 having asignificantly longer stroke than the tag axle gas springs 216. Wherebythe tag axle 106 will continue to support the truck frame when one ormore of the pusher axles 24 with their gas spring suspension systemscannot.

For example, one or more of the pusher axles 24 may loose their loadsupporting ability because of the loss of the weight or reactive forceacting on their gas springs 44 when the associated pusher axle tires 42encounters a road dip exceeding 3.7-inches in depth. While the tag axle106 will not because of the combined operation of the primary andsecondary tag axle suspension in the tag axle suspension system 108.

Moreover, the arrangement of the tag axle gas springs 216 in thesecondary tag axle suspension of the tag axle suspension system 108contribute to a significant degree in aid of the other axle suspensionsystems in that they directly accept and support lateral forces orloading on the truck frame 16 and while absorbing shock loading incurredat the tag axle wheels 110 on encountering road depressions such aspotholes thereby effectively preventing transmission of such to thetruck frame as described earlier. As well as assist the other axlesuspension systems in stabilizing and maintaining the truck frame at thedesired substantially level attitude with respect to the road surfaceand with and without a payload.

It will also be appreciated that the tag axle gas springs 216 by theirarrangement with respect to the centrally pivoted tag axle 106 in closeproximity to the tag axle pivot pin 150 are strategically located tovery efficiently support lateral loading (roll-directed or tilt loading)on the truck frame transmitted through the long suspension arms 134 tothe tag axle. And it will also be appreciated that the tag axle gassprings 216 by their relatively small size and arrangement as comparedto the pusher axle gas springs provide a very compact secondary tag axlesuspension in the immediate vicinity of the tag axle characterized bythe small space required as compared to the much larger space that wouldbe required for gas springs like those commonly used for the pusheraxles.

The tag axle gas springs 216 also have significantly smaller springcompliance than the leaf spring suspension system 26 serving the steeraxle 20 but a slightly larger spring compliance compared with the leafspring suspension system 28 serving the drive axles 22 in providing acompatible multiaxle suspension arrangement for supporting the truckframe. Wherein the leaf spring suspension systems 26 and 28, like thegas spring suspension systems 30 of the pusher axles, accept andaccommodate pitching and laterally directed loading or forces on thetruck frame 16 as well as road bumps and depressions and holes. And inthe exemplary embodiment, the leaf spring steer axle suspension 26 hasabout a 5.25-inches spring compliance as limited by bump stops (notshown) to accommodate this amount of up and down movement of the steerwheels 32 relative to the truck frame. While the leaf spring drive axlesuspension 28 have only about a 2.0-inches spring compliance (1.0-inchesamplitude) as limited by bump stops (not shown) accommodating this smallamount of conjoint up and down movement of the steer axle wheels 32relative to the truck frame 16 but being of the walking beam typeaccommodate with their walking beams 43 about 10.0-inches up and downmovement (5.0-inches amplitude) of either one of the drive axles 22 andits associated wheels 34 relative to the truck frame on encountering abump or road depression or pothole.

Furthermore, the tag axle gas springs 216 with their spring compliancethat is significantly less than that of the steer axle suspension 26 andpusher axle suspensions 30 but considerable more than that of the driveaxle suspension 28 act to establish the tag axle 106 when deployed as astabilizing platform similar to that of conventional truck outriggers inresisting roll (tilting) of the truck frame about the roll axis 46.Wherein it will be understood that in such comparison, such outriggersare only employed when the truck is stationary.

For example, in the case of a truck carrying a crane, such outriggersare employed to prevent the crane and the supporting truck from tippingover when the crane is working with a heavy load remote from the truckand especially where the load is either side of the truck's roll axis.The tag axle gas springs 216 operate in a similar manner in contributingto the lateral stability of the truck frame in that with the truckstationary and when one of these gas springs is loaded more than theother because of tilting forces on the truck frame 16, the other gasspring is correspondingly relieved of lateral load and the tag axle tireon this side can be pressured up to help balance the load on both of thetag axle gas springs and thus help level and stabilize the truck frameunder such an imbalanced lateral load condition such as during loadingof the truck body and for travel with the load to a delivery site.

In substantial contrast with respect to the steer axle and drive axleleaf spring suspension systems 26, 28 and the pusher axle gas springsuspension systems 30 and also the tag axle gas springs 216, the primaryactuators 158 in providing the spring compliance in the primary tag axlesuspension in the tag axle suspension system 108 allow considerably moreup and down movement of the tag axle wheels 110 than that allowed of thesteer axle wheels 32, drive axle wheels 34 and pusher axle wheels 36 bytheir respective axle suspension systems 26, 28, 30 and that allowed ofthe tag axle wheels 110 by the gas springs 216 in the secondarysuspension of the tag axle suspension system 108.

For example, in the exemplary embodiment the primary suspension in thetag axle suspension system 108 acting through the primary actuators 158provides a spring compliance that allows up and down movement of the tagaxle 106 and thus the tag axle wheels 110 totaling about 72.0-inches(36.0-inches amplitude) with the mean determined with the truck and tagaxle on a level surface. Whereas the secondary tag axle suspensionacting through the tag axle gas springs 216 and while pressured downforce is maintained on the tag axle as described later allows only about4.6-inches total up and down movement (2.3-inches amplitude) of the tagaxle wheels or about 0.06% (4.6/72.0) of that allowed by the primaryactuators 158 on a comparative spring compliance basis in relation tototal up and down tag axle wheel movement.

Whereby the tag axle suspension system 108 with the primary tag axlesuspension that includes the primary actuators 158 can effectivelyaccommodate elevation differences up to about 36.0-inches between thetag axle wheels 110 and the other axle wheels 32, 34, 36 and with thesecondary suspension that includes the gas springs 216 and centrallypivoted tag axle 106 can effectively accommodate bumps about 2.3-incheshigh and depressions or holes about 2.3-inches deep at the individualtag axle wheels while maintaining the tag axle tires 112 in load bearingcontact with the road. And wherein maximum advantage is taken of thelarge spring compliance provided by the primary tag axle suspension inthe tag axle suspension system 108. Such as when the truck passes over avery low dip in a road. Or when the truck passes over a very high risein a road such as in crossing over a dike or an elevated railroadcrossing wherein the tag axle 106 continues to be forced to help supportthe truck frame under such an extreme road condition as shown in FIG.12.

The establishment of the tag axle 106 in the stored inactive conditionand in the deployed active condition is controlled and established by atag axle operating system comprising the electrical circuitry in FIG. 23and the hydraulic fluid-gas circuitry in FIG. 24 where the later isshown as conditioned in establishing the tag axle in a stored inactivecondition, is shown in FIG. 25 as conditioned in establishing the tagaxle in an active condition, and is shown in FIG. 26 as conditioned inestablishing the tag axle in a force-relieving condition/tag axlebrake-disabling condition. And to which reference will be made infurther describing the tag axle operation as well as describing thecircuitry.

Referring first to the electrical circuitry in FIG. 23, the circuitryincludes the truck's battery 223 and Ignition Switch 224, an Up/DownSelector Switch 226, a Mode Selector Switch 228, an Up Pressure Switch230, and a Down Pressure Switch 232. Wherein the Selector Switches 226and 228 together with a Hydraulic Pressure Gage 234 (see FIG. 23) arelocated in a separate control panel (not shown) in the cab 12. Andwherein the Up Pressure Switch 230, the Down Pressure Switch 232 and theHydraulic Pressure Gage 234 are connected to receive hydraulic pressurein the hydraulic fluid/gas circuitry shown in FIGS. 24-26 where they arealso labeled as “UPSw”, “DPSw” and “HPG”, respectively.

The Up/Down Selector Switch 226 is a manually controlled three-positionswitch that is moveable to and can then be locked in three positionslabeled “Up”, “Neutral” and “Down” in FIG. 23. The Mode Selector Switch228 is also a manually controlled three-position switch that is moveableto three positions labeled “Manual”, “Off” and “Auto” in FIG. 23 and iseither momentarily positioned in the Manual position or moved and lockedin either the Off position or Auto position. The Selector Switches 226and 228 are connected in the electrical circuitry for effecting powerdelivery to six solenoid valves including the solenoid valve 132 whichare connected in the hydraulic fluid/gas circuitry as shown in FIGS.24-26, are hereinafter referred to as the Tag Axle Brake Valve 132, UpValves 236 and 238, Down Valves 240 and 242, and Dump Valve 244 and arealso so-labeled in FIG. 23. And wherein without power supplied to thesevalves, the Tag Axle Brake Valve 132, Up Valves 236 and 238, and DownValves 240 and 242 are normally closed and the Dump Valve 244 isnormally open. And wherein the contacts in the Up Pressure Switch 230below a certain pressure are closed as shown to delivery power to theDump Valve 244 below this pressure via the Up/Down Selector Switch 226and the contacts in the Down Pressure Switch 232 below a certainpressure are closed with respect to the Dump Valve 244 and open withrespect to the Tag Axle Brake Valve 132 as shown to thereby deliverpower to the Dump Valve via the Up/Down Selector Switch 226 whilepreventing power delivery to the Tag Axle Brake Valve below thispressure.

Referring now to the hydraulic fluid/gas circuitry in FIGS. 24-26, thiscircuitry further includes a hydraulic pump 246 also labeled as “P” inthese Figures that is driven by the engine 50 and draws hydraulic fluidof a suitable type from a sump 248 that is vented to atmosphere anddelivers the fluid under pressure to a system main line 250. Wherein themaximum pressure is limited in the main line 250 to an acceptable ortolerable pressure by a System Pressure Relief Valve 252 that exhaustsfluid from the main line 250 back to the sump via a system return line254.

Describing first the conditioning of the tag axle 106 in its storedinactive condition in the Auto mode and with reference to FIGS. 23 and24 and which involves raising the long suspension arms 134 andeventually pivoting the short suspension arms 140 in the same pivotaldirection as the long suspension arms, the vehicle operator with theIgnition Switch 224 turned on and the engine 50 running, moves theUp/Down Selector Switch 226 from the Neutral position to the Up positionand locks it in this position and moves the Mode Selector Switch 228from the Off position to the Auto position and locks it in this positionPower is then delivered to the Up Valves 236 and 238 to open thesevalves. While the contacts in the Up Pressure Switch 230 are thenconditioned as shown in FIG. 23 to deliver power to the Dump Valve 244that without power is normally open as shown to thereby condition it inits closed condition until a certain prescribed pressure is reached andsensed at the Up Pressure Switch 230 as described later. Power is alsothen available to the Dump Valve 244 via the Down Pressure Switch 232but as described later this switch opens to the Dump Valve before the UpPressure Switch 230 opens to finally interrupt power to the Dump Valvein establishing the tag axle in its inactive stored condition.

Without power to the Down Valves 240 and 242, they remain closed andhydraulic fluid is delivered from the main line 250 at a constant flowrate to the Up Valve 236 by a Flow Control Valve 256 that returns excessflow to the sump 248 via the system return line 254. The fluid at asuitable constant flow rate is then delivered through the open Up Valve236 to a delivery/return line 258 where the fluid passes through a CheckValve 260 and then directly to the chamber 214 in the toggle cylinder160. And wherein in the exemplary embodiment, the Flow Control Valve 256is set to regulate the flow delivery rate to about three to five gallonsper minute (3-5 gpm).

Fluid after passing through the Check Valve 260 also passes throughsecond Check Valves 262 in parallel branches of the delivery/return line258 and then directly to the hydraulic chamber 184 in the primaryactuators 158 where the fluid pressure acts on the primary actuatorpistons 166. With fluid passing through the Check Valve 260 alsodelivered by a Shuttle Valve 264 to a signal line 266 that is connectedto both the Up Pressure Switch 230 in the electrical circuit and theHydraulic Pressure Gage 234 in the cab 12.

The other hydraulic chamber 180 in the primary actuators 158 are thenopen to the sump 248 via the other open Up Valve 238, a delivery/returnline 268 and the system return line 254. Fluid remaining in the chambers180 from tag axle lowering operation as described later is thusexhausted as the primary actuator piston rods 170 are forced by therespective pistons 166 to retract by the hydraulic fluid being suppliedunder pressure via the delivery/return line 258 to the other primaryactuator hydraulic chambers 184. Whereby the tag axle 106 is raised bythe long suspension arms 134 from its fully lowered position through anintermediate position shown in FIGS. 16 and 17 and then to the positionshown in FIG. 18 on full retraction of the primary actuator piston rods170 (see FIG. 24) and wherein the long suspension arms 134 are thenupright and the toggle cylinder 160 has not yet toggled the tag axle 106into its stored location.

During the tag axle lifting operation with the long suspension arms 134,the gas pressure in the primary actuator gas chambers 186 acts on theprimary actuator accumulator pistons 174 and with the long suspensionarms 134 in their upright position and the primary actuator piston rods170 fully retracted with the hydraulic pressure in chambers 184exhausted, the accumulator pistons are forced by the initial chargingpressure in the gas circuit to be positioned with their hydraulic fluidexposed face bottomed on the respective primary actuator hydraulicpistons 166 as shown in FIG. 24.

The other chamber 212 of the toggle cylinder 160 during the raising ofthe long suspension arms 134 is blocked from the open Up Valve 238 viathe delivery/return line 268 by a Check Valve 270 and a pilot-controlledFlow Relief Valve 272 which are connected in parallel between thehydraulic chamber 212 and the delivery/return line 268. The Flow ReliefValve 272 receives its pilot pressure signal from the delivery/returnline 268 that is then open to the vented sump 248 via the open Up Valve238. And without its pilot pressure signal, the Flow Relief Valve 272 isnormally closed and is set to open as shown in FIG. 24 at apredetermined pressure at the toggle cylinder hydraulic chamber 212 andthereby establish its connection with the sump 248 via the open Up Valve238 and only then allow the toggle cylinder piston rod 196 to retract bythe fluid under pressure being supplied to the other toggle cylinderhydraulic chamber 214. With this occurring when the primary actuatorpiston rods 170 are fully retracted and locating the long suspensionarms 134 in their upright position while the pressure in the togglecylinder chamber 214 as well as in the primary actuator chambers 184rises to the full pressure available in the delivery/return line 258 andurges retraction of the toggle cylinder piston rod 196 while the othertoggle cylinder chamber 212 is then still blocked from the otherdelivery/return 268 by the Flow Relief Valve 272.

In the exemplary embodiment, the Flow Relief Valve 272 is set to openwithout its pilot pressure signal at about 875-psi to open the togglecylinder chamber 212 to the delivery/return line 268 to only then allowthe pressure acting in the other toggle cylinder chamber 214 to retractthe toggle cylinder piston rod 196 and toggle the tag axle 106 into itsstored location over the rear end of the truck body as shown in FIGS. 19and 20. Wherein the long suspension arms 134 remain in their uprightposition and the short suspension arms 140 have been forced by thetoggle cylinder linkage 161 with the toggle cylinder piston rod 196 toswing or toggle the tag axle on the short suspension arms 140 into itsstored location. And with the Flow Relief Valve 272 thus delaying theretraction of the toggle cylinder piston rod 196 in a sequencing manneruntil the long suspension arms 134 are upright before toggling the tagaxle 106 into its stored location and into a folded-in relationship tothe upright long suspension arms 134 and over the truck body. Andwherein this folded-in relationship of the tag axle in the storedlocation minimizes the height of the tag axle wheels 110 above the truckbody and the pressure in the toggle cylinder chamber 214 and primaryactuator hydraulic chambers 184 are at the full pressure available inthe delivery/return line 258.

The Down Pressure Switch 232 is exposed to the pressure in thedelivery/return line 158 during the raising of the tag axle but is setto open in respect to the Dump Valve 244 to interrupt power thereto at acertain predetermined pressure for conditioning the tag axle in itslowered active condition as described in more detail later. And the UpPressure Switch 230 is set to operate at a significantly higherpredetermined pressure in the delivery/return line 258 to thus open tothe Dump Valve 244 and interrupt power thereto after the Down PressureSwitch 232 has interrupted power thereto and thereby finally interruptpower to the Dump Valve 244. And without power, the Dump Valve 244 iscaused to open as shown in FIG. 24 and thereby connect the system mainline 250 to the sump 248 via the system return line 254 and therebybypass discharge from the pump directly back to the sump to relieve thepump of unnecessary duty. And when this bypass flow by the Dump Valve244 occurs, the pressure in the system main line 250 drops and the CheckValve 260 in the delivery/return line 258 then prevents backflow throughthe open Up Valve 230 with the open Dump Valve. And wherein this bypassflow is free of restriction by pilot-operated primary actuator LoadLocking Valves 274 that are connected in parallel with the Check Valves262 between the respective primary actuator hydraulic chambers 184 andthe delivery/return line 258 and perform no function in the raising ofthe tag axle.

In the exemplary embodiment, the Up Pressure Switch 230 is set tofinally interrupt power to the Dump Valve 244 and thus effect openingthis valve for bypass flow at a pressure of about 2,000-psi in thedelivery/return 258 with this occurring when the primary actuator pistonrods 170 and the toggle cylinder piston rod 196 are fully retracted andthe pressure on their pistons then increases to this pressure. And thispressure at 2,000-psi as determined by the Up Pressure Switch 230 isthen trapped in the primary actuator hydraulic chambers 184 by the CheckValve 260 thereby locking the primary actuators piston rods 170 in theirfully retracted condition. And wherein this pressure of 2,000-psi isalso trapped in the toggle cylinder chamber 214 by the Check Valve 260while the Flow Relief Valve 272 has then closed and traps the 875-psipressure in the other toggle cylinder chamber 212 against the higher andopposing pressure of 2,000-psi thereby locking the toggle cylinderpiston rod 196 with the pressure differential (2,000-psi minus 875-psior 1,125-psi) in its fully retracted condition as shown in FIG. 24. Andwith these pressure-locking conditions, the tag axle 106 is therebylocked in its stored inactive condition above the end of the truck bodyand with the tag axle brakes disabled in that with the Up/Down SelectorSwitch 226 in the Up position, power is not available to the Tag AxleBrake Valve 132 so it remains normally closed preventing air pressuresupply to the tag axle brakes 114.

Describing now the conditioning of the tag axle 84 in its lowered andactive condition and with reference to FIGS. 23 and 25 and starting withthe tag axle 106 in its raised and stored inactive condition asdescribed above, the vehicle operator moves the Up/Down Selector Switch226 from the Up position through the Neutral position to the Downposition and locks it in this position while leaving the Mode SelectorSwitch 228 in the Auto position. Thereby delivering power to the DownValves 240 and 242 to open these valves as shown in FIG. 25 while the UpValves 236 and 238 are then without power and thus closed as shown.

The contacts in the Down Pressure Switch 232 are conditioned to deliverpower to the Dump Valve 244 to close this valve until a certainprescribed pressure is reached and not deliver power to the Tag AxleBrake Valve 132 so that this valve remains closed to disable the tagaxle brakes 114 until this prescribed pressure is reached. And withdelivery of power to the Dump Valve 244 via the Down Pressure Switch232, power is prevented by a diode 278 from reaching the Up Valves 236and 238 via the normally closed Up Pressure Switch 230 so that theyremain closed.

Hydraulic fluid from the pump 246 then passes from the main line 250through the open Down Valve 240 to the delivery/return line 268 where itpasses through a Check Valve 280 and then through the Check Valve 270 tothe toggle cylinder chamber 212 where pressure has been contained at875-psi by the Flow Relief Valve 272 with the tag axle in the inactivecondition. While fluid passing through the check valve 280 is alsodelivered to the primary actuator hydraulic chambers 180 and via theShuttle Valve 264 to the signal line 266 and thus to the Down PressureSwitch 232 and the Hydraulic Pressure Gage 234. While the other openDown Valve 242 then connects the other delivery/return line 258 to thesystem return line 254 and thereby connects the other toggle cylinderchamber 214 to the sump 248 to thus exhaust this chamber.

The fluid delivery to the primary actuator hydraulic chambers 180 forcestheir respective piston rods 170 to start extending and thereby lowerthe long suspension arms 134 from their upright position while the fluiddelivery to the toggle cylinder chamber 212 starts forcing the togglecylinder piston rod 196 to extend and acting through the toggle linkage161 swing the tag axle 106 on the short suspension arms 140 relative tothe long suspension arms 134 in an unfolding direction opposite that inlocating the tag axle in its stored location. The Flow Relief Valve 272now receives a piloting pressure from the delivery/return line 268 andwherein this valve is set to close when the pressure reaches about500-psi in the toggle cylinder chamber 212 and with such valve closureand together with the check valve 270 traps this pressure in the chamber212 so that it remains throughout the lowering of the tag axle with thefluid pressure being supplied to the primary actuator chambers 180.

The Load Locking Valves 274 also receive a piloting pressure from thedelivery/return line 268 and at about 1,700-psi they are set to closeand together with the respective Check Valves 262 trap this pressure inthe primary actuator chambers 184 throughout the lowering of the tagaxle with the fluid being supplied to the other primary actuatorchambers 180 by the delivery/return line 268. Whereby with continuedlowering of the tag axle, the toggle cylinder piston rod 196 with the500-psi in its chamber 212 is fully extended thereby unfolding the tagaxle 106 with respect to the long suspension arms 134 with togglingaction of the toggle linkage 161 when these arms reach an angle of about30-degrees from horizontal as shown in FIG. 21 and thus prior to thesearms and thereby the tag axle reaching their fully lowered positionshown in FIG. 22. And wherein the toggle linkage 161 has beenestablished in its over-center condition to accept the resulting loadingplaced on the tag axle with the tag axle tires being forced to bearagainst the road surface.

The initial charge pressure of the nitrogen in the exemplary embodimentis such that the pressure in the primary actuator gas chambers 186 isthen at a certain pressure and acts on the respective accumulatorpistons 174 as the tag axle tires 112 are forced against the road by thepressure building in the delivery/return line 268 to the primaryactuator chambers 180. With this hydraulic pressure thus being inopposition to the nitrogen pressure also acting on the accumulatorpistons.

The Down Pressure Switch 232 is exposed to the hydraulic pressure in thedelivery/return line 268 and is set at a certain prescribed pressure inthis line to interrupt the power to the Dump Valve 244 to thus open thisvalve as shown and thereby establish this pressure as the operating orworking pressure in the delivery/return 268 and at the same time deliverpower to the Tag Axle Brake Valve 132 to open this valve as shown inFIG. 8 and enable the operation of the tag axle brakes 114. And whereinwith the Dump Valve 244 open, fluid is bypassed to the sump dropping thepressure in the system main line 250 like in the establishment of thetag axle in the inactive condition but in this case with the Down Valve240 open and with the Check Valve 280 then preventing backflow throughthis open Down Valve to contain this working pressure in thedelivery/return line 268.

In the exemplary embodiment, the Down Pressure Switch 232 is set tointerrupt power to the Dump Valve 244 to open this valve and to deliverpower to the Tag Axle Brake Valve 132 to open this valve and enable thetag axle brakes 114 when the hydraulic pressure in the delivery/returnline 268 and thus acting in the hydraulic chambers 180 on the respectivehydraulic pistons 166 and also on the respective accumulator pistons 174reaches about 1,525-psi as the prescribed operating or working pressure.And for establishing the tag axle 106 in its active condition, the gasportion of the hydraulic fluid/gas circuitry is initially charged withnitrogen at a pressure that is about 85-87 percent of the desiredoperating or working pressure in the delivery/return line 268 and thusfor example at the low end of this range is about 1,300-psi. With thenitrogen charging being accomplished in setting up the gas portion ofthe system by moving the Mode Selector Switch 228 to the Off positionand then moving the Up/Down Selector Switch 226 to the Up position forthe nitrogen charging to occur. And wherein the nitrogen pressure canalso be checked later and recharged if necessary by following the samecontrol switch procedure.

With the truck on a level surface as shown in FIGS. 1 and 22, the tagaxle 106 is fully forced or pressured down after its tires 112 contactthe supporting surface and the pressure in the delivery/turn line 268reaches the prescribed working pressure of 1,525-psi. Wherein the longsuspension arms 134 are then substantially parallel to the road andsubstantially level with the truck frame, the pivot axis of the tag axle106 is also substantially parallel to the road, and both the primaryactuator hydraulic pistons 166 and accumulator pistons 174 are then intheir mean operating position as shown in FIGS. 6 and 25. And whereinwith respect to the primary suspension of the tag axle, the operatingpressure in the delivery/return line 268 and thus available to thechamber 180 of the primary actuators 158 is 1,525-psi and wherein thepressure in the other hydraulic chambers 184 is limited by thepilot-operated Load Locking Valves 274 and 274 to 1,700-psi by pilotingpressure received from the delivery/return line 268 to hydraulicallyforce balance the primary actuator hydraulic pistons 166 in their meanposition and thereby their respective piston rods 170. Noting that theface of the hydraulic pistons 166 exposed to the respective hydraulicchambers 184 is slightly smaller in area than their face exposed to theother hydraulic chambers 180 and with the difference in pressure ofabout 175-psi between the higher pressure of 1,700-psi in chambers 184and the lower operating pressure of 1,525-psi in chambers providing forsuch hydraulic force balance on the pistons 166.

The hydraulic pressure in the delivery/return line 268 in reaching theoperating pressure of 1,525-psi as determined by operation of the DownPressure Switch 232 over comes the opposing nitrogen pressure of1,300-psi on the accumulator pistons 174. And thereby forces movement ofthe accumulator pistons 174 from their bottomed position on therespective hydraulic pistons 166 shown in FIG. 24 with the longsuspension arms 134 upright to their mean position shown in FIG. 25 andthereby compressing the nitrogen gas that was initially at a pressure of1,300-psi to a significantly higher pressure. And wherein the meanposition of the accumulator pistons 166 occurs where the workinghydraulic pressure of 1,525-psi is balanced or offset by the forcedincrease of nitrogen pressure that is then also at the same pressure inproviding the balanced pressure on the accumulator pistons as shown inFIG. 25.

In the active condition in the exemplary embodiment with the prescribedworking pressure of 1,525-psi, the tag axle is forced to accept a loadof about 12,000-pounds that is about 1,200-pounds less than the13,200-pounds rated load capacity of the tag axle. And it will beunderstood that the load placed on the tag axle can be increased butpreferably still below the rated load capacity of the tag axle byincreasing the working pressure by setting the Down Pressure Switch 232to operate as before but at a higher pressure.

With the tag axle thus established in the active condition and with thetruck on a level road surface and the primary actuator hydraulic pistons166 and accumulator pistons 174 in their mean operating positions, theprimary actuators 158 operate with both hydraulic pressure and gaspressure to allow the tag axle 106 to raise and lower to the largedegree described above by pivoting of the long suspension arms 134coupled with gas spring action acting through the accumulator pistons.Wherein the pilot operated Load Locking Valves 274 open the primaryactuator chambers 184 to the delivery/return line 268 when the pressurein the other primary actuator chambers 180 reaches a predeterminedpressure in allowing the gas spring operation and which in the exemplaryembodiment is set to occur when the hydraulic pressure reaches about800-psi to 1,000-psi in the latter chambers. While the nitrogen beingcompressible acts to maintain the operating pressure as the tag axle isforced to rise and lower.

For example, the primary actuator piston rods 170 will move inward inrespect to their cylinder 162 and then return outward to their meanposition with gas spring action when the tag axle wheels 110 pass over abump on the supporting surface and will move outward in respect to theircylinder and return inward to their mean position with gas spring actionwhen the tag axle wheels pass through a dip in the supporting surface.And wherein the piloted Load Locking Valves 274 operate as describedabove should the pressure reach about 800-psi to 1,100-psi in theprimary actuator chambers 180 to allow this suspension action. And withthe same operation in play regardless of the height of the bump or depthof the dip up to the limits of the up and down movement allowed of thetag axle which as earlier described is about a 36.00-inches amplitudeand includes the ability to traverse a significantly raised section suchas when passing over an elevated train crossing as shown in FIG. 12 withthe tag axle continuing to accept its prescribed load.

In further regard to the raising of the tag axle under load and onencountering an unusually high portion of the supporting surface wherethe tag axle 106 attempts to raise higher than about 36.00-inches innegotiating such an unusually high portion thereby forcing the primaryactuator piston rods 170 into their cylinders 116 an unusual distance, aHigh Pressure Relief valve 282 opens at a predetermined pressureconnecting the delivery/return line 268 to the system return line 254 tothereby limit the operating or working pressure in the delivery/returnline 268 to a suitable level still within the load capability of the tagaxle. In the exemplary embodiment, the High Pressure Relief valve 282 isset to open at about 1,950-psi or about 425-psi above the operatingpressure of about 1,525-psi to thus limit the maximum down force thatcan act on the tag axle under such a circumstance and is still withinthe maximum load capability of the particular tag axle construction. TheHigh Pressure Relief Valve 282 also provides an additional function inthat it will open at this pressure setting to guard the tag axleoperating system and the truck frame from hydraulic pressure spikes thatcan result from the tag axle wheels encountering for example severepotholes and extremely rough railway crossings.

In addition, a Low Nitrogen Pressure Switch 284 also labeled as “LNPS”is connected to the delivery/return line 268 and operates to alert thevehicle operator with both sound and visual alarms (not shown) locatedin the cab 12. For example, in the event that the nitrogen pressure inthe gas circuitry is lost for some reason, the hydraulically pressuredaccumulator pistons 174 in the primary actuators 158 on the loss of thenitrogen pressure will bottom with significant impact at the closed endof their respective bores 172 in the primary actuator piston rods 170causing a pressure spike in the hydraulic fluid pressure in thedelivery/return line 268. And in the exemplary embodiment, the LowNitrogen Pressure Switch 284 is normally open and set to operate at apressure of about 1,850-psi or about 100-psi below the setting of theHigh Pressure Relief Valve 282 and on sensing such a pressure spike asbeing indicative of low nitrogen pressure then closes in a releasablelocked condition and triggers the sound and visual alarms indicating lownitrogen pressure to the vehicle operator. Thereby giving the operatorreason to place the tag axle in its stored inactive condition until thissituation is remedied.

Having described the operation with the Up/Down Selector Switch 226 inthe Down position and the Mode Selector Switch 228 in the Auto position,the truck operator can adjust the down force on the tag axle during itslowering so as to accept less load than that provided in the Auto modeas for example when there is no payload or only a partial one. This isaccomplished by the operator placing the Up/Down Selector Switch 226 inthe Down position and moving the Mode Selector Switch 228 from the Offposition to the Manual position while monitoring the Hydraulic PressureGage 234. The Dump Valve 244 is then closed and when the pressureindicated on the Hydraulic Pressure Gage 234 reaches a pressure deemedsufficient to load the tag axle under the circumstances and which willbe less than that in the Auto mode, the operator then releases the ModeSelector Switch 228 that then automatically returns to the Off positionwhereby power is interrupted to the Dump Valve 244 thus opening thisvalve and with the selected operating pressure maintained in thedelivery/return line 268 by the Check Valve 280 with the Down Valve 240open. And wherein this lesser operating pressure (less than the1,525-psi in the Auto mode) thus applies less down force on the tag axlethan in the Auto mode as determined by the truck operator.

It will also be appreciated from the above-described operation of theMode Selector Switch 228, that the tag axle 106 cannot be raised orlowered with the Mode Selector Switch in the Off position. Regardless ofwhether the Up/Down Selector Switch 226 is in the Up position or theDown position because the Dump Valve 244 is then without power and isthus open preventing pressure buildup in either the supply/delivery line258 or 268.

In the Auto mode and with respect to tag axle brake operation, the DownPressure Switch 232 delivers power to open the Tag Axle Brake Valve 132and enable the tag axle service brakes 114 only when a certain pressureis reached in the delivery/return line 268 and thus indicating the tagaxle is in its normally forced active condition helping to support thetruck frame. And in the exemplary embodiment this occurs with a workingpressure of about 1,525-psi in the delivery/return line 268 as describedearlier. As a result and in the event the vehicle operator deploys thetag axle while driving along a road and the tag axle is not yet fullyestablished in its active condition with the 1,525-psi working pressureand should the operator in the interim then have to apply the vehiclebrakes for some reason such as on encountering a stop light, stop signand interfering traffic, the tag axle service brakes 114 are not yetenabled. And thus the tag axle wheels will be in a free wheel mode whentheir tires contact with the road to thereby help prevent these tiresfrom being flat spotted in such a situation.

Enabling and disabling of the tag axle service brakes 114 and alsorelieving the pressure and thus the down force applied to the tag axlebut without raising the tag axle 106 is provided under certaincircumstances by operation of two like proximity switches 286 of themagnetically operated type referred to as magnetic proximity sensorswhich are operatively associated with the tag axle 106 and located onopposite sides of the tag axle pivot pin 150 between this pivot and thenear tag axle wheel 110. The proximity switches 286 have normally closedcontacts that break contact or open when the switches come into closeproximity to an associated magnet 288 that thus serves as a switchoperator to break contact or open the switch. With the proximityswitches also referred to herein to as Tag Axle Tilt Sensors and also solabeled in FIG. 23.

Referring to FIGS. 4, 27 and 28, the proximity switches 286 and theirrespective magnets 288 are located between the respective tag axle gassprings 216 and the tag axle pivot pin 150 respectively. Wherein theproximity switches 286 are supported on the tag axle carriage 146 with asupport arm 290 that is fixed with a pair of bolts 291 to the rear side292 of the carriage directly above the respective arms 157 for the coilspring/shock absorber assemblies 123 which are fixed to this side. Theproximity switches 286 extend through the respective support armssupport arms 290 and have an externally threaded portion whereby theyare fastened in place with washers and nuts 294 on opposite sides of thearms such that a cylindrical portion 296 of the switch enclosing themagnetically operated switch contacts is arranged for exposure to therespective magnets 288. And wherein the nuts 294 also provide for fineadjustment of the face-to-face spacing between the cylindrical portion296 and the respective magnet 288 to effect switch operation. Andwherein side-to-side adjustment between the cylindrical portion 296 ofthe proximity switches 286 and their respective magnets 288 in the pathof travel of the proximity switches is also provided by slots 297 in thearms 290 that receive the bolts 291. And wherein adjustment with respectto the travel of the proximity switches 286 is also provided by slots299 in the arms 290 that receive the cylindrical portion 296 of theproximity switches 286. See FIGS. 28 and 30.

The magnets 288 have a rectangular shape and are fixed by a single,non-magnetic stainless-steel taper-headed bolt 298 to the rear side 300of the tag axle trunnion body 148. Wherein the head of the bolts 298 isflush with the face of the magnets and a thin cushion 302 in the form ofdouble-sided tape about 0.075-inches thick is sandwiched between themagnets 288 and the side 300 of the trunnion body 148 to cushion themagnets during their securing to prevent their fracture on tightening oftheir fastening bolt 298. With the double-sided tape 302 providing anaddition function in that it allows the use of only a single fastener inretaining each magnet in a desired attitude with respect to the path oftravel of the proximity switches which has the short dimension of therectangular-shaped magnets extending along this path and their longdimension or width extending transverse of this path to provide arelatively limited magnetic force field for the size of the magnet inthis direction for tripping the proximity switches.

The magnets 288 are located on the trunnion carriage 146 so as to lie inthe path of travel of the respective proximity switches 286 with tiltingmovement of the tag axle about the tag axle pivot pin 150 as laterdescribed. And to this end, the proximity switches 286 and theirrespective operating magnets 288 are located at like distances from andclose to the tag axle pivot pin 150 so that the degree of tilting orpivotal movement about the tag axle pivot pin required to effectswitching operation by their associated magnets is thereby minimized.And wherein certain prescribed tilting of the tag axle about the pivotpin 150 in one direction brings one of the proximity switches 286 inclose proximity to its associated magnet 288 to break (open) contact inthe switch and tilting of the tag axle in the opposite direction to thesame degree operates the other proximity switch in like manner.

As shown in FIG. 23 and with the tag axle 106 in its active conditionand in a level attitude with the road surface, the contacts in theproximity switches 286 are closed and complete a circuit from theControl Switch 226 while in the Down position to a relay 304 to hold therelay contacts open and thereby open a circuit from the battery 223 tothe Up Valves 236 and 238 to prevent power thereto so that the pressureddown force is maintained on the tag axle and the Tag Axle Brake Valve132 remains open as shown in FIG. 8 to make air pressure available toapply the tag axle service brakes 114. But when the contacts in eitherof the proximity switches 286 are broken, the relay 304 is no longerpowered and its contacts close to then deliver power to both the UpValves 236 and 238 to open these valves while the Down Valves 240 and242 are open to thereby relieve the hydraulic-gas pressure producedforce on the tag axle 106 but without raising the tag axle 106 byoperation of the primary actuators 158.

This condition being shown in FIG. 26 and wherein the delivery/returnline 268 is then connected by the Up Valve 238 to the system return line254 and thus exhausting the working pressure that existed in thedelivery/return line 268 and thus while the other delivery/return 258 isalso connected to the system return line. Whereby the pressured downforce on the tag axle 106 is relieved with the absence of the workingpressure while the toggle cylinder 160 with the 500-psi pressure lockedin the chamber 212 continues to hold the tag axle in position relativeto the long suspension arms 134 and the Down Pressure Switch 232 withoutthe working pressure then operates to interrupt power to the Tag AxleBrake Valve 132 thus closing this valve and disabling the tag axlebrakes 114. And wherein the tag axle 106 is not raised with the loss ofworking pressure with the opening of the Up Valves 236 and 238 while theDown Valves 240 and 242 are open. And without the hydraulic-gas pressureproduced force, the tag axle 106 no longer helps to the support thetruck frame 16 and the tag axle wheels 110 then only bear the deadweight of the tag axle assembly with the tag axle tires 112 remaining incontact with the road. And without the working pressure in thedelivery/return line 268 and thus in the primary actuator chambers 180,the accumulator pistons 174 are forced by the nitrogen pressure tobottom on and be contained by the respective primary actuator pistons166 as shown in FIG. 26.

Moreover, with the loss of working pressure in the delivery/return line268, the Down Pressure Switch 232 then delivers power to the Dump Valve244 and thus closing this valve as shown in FIG. 26. Whereby the DumpValve 244 is in a ready condition to provide for rapid re-establishmentof the working pressure in the delivery/return line 268 should theproximity switch that was opened be reestablished in its closedcondition and thereby interrupt power to the Up Valves 236 and 238 toclose these valves to thereby effect restoration of the tag axle in itsactive condition.

For performing the desired action of relieving the down force on the tagaxle 106 and disabling the tag axle wheel service brakes 114 undercircumstances as described later, the proximity switches 286 and theirrespective operating magnets 288 are located relative to each in likemanner with the magnets positioned below and distant from theirrespective switches 286 when the tag axle 106 is in a normal levelattitude (horizontal to the road). Wherein the magnets 288 are thensufficiently distant from their respective proximity switches 286 as tonot open or break their contacts and thus maintain the relay 294 open.See FIGS. 28-30.

In the exemplary embodiment, the relative locations of the proximityswitches 286 and their magnets 288 are set so that when the tag axle 106tilts or swings from its normal level position in either directionthrough an angle of 3.5-degrees that as earlier described translates to2.3-inches of downward movement of one of the tag axle wheels 110 andthe same amount of upward movement of the other tag axle wheel, thecontacts in one of the proximity switches will be broken by its thenclose proximity to its operating magnet thus closing the relay 304 anddelivering power to the Up Valves 236 and 238 to relieve the pressureddown force on the tag axle and thereby disable the tag axle wheelservice brakes through opening of the Down Pressure Switch 182 inrelation to the Tag Axle Brake Valve 132. And wherein this allowed upand down tag axle wheel amplitude of 2.3-inches before one of theproximity switches 286 is tripped is determined to be less than theradial dimension of the tag axle tires 112 outward of the tag axlewheels 110 to prevent damage to these wheels in the event one of thesetires deflates as described in more detail later.

Describing now the operation of the proximity switches 286, their switchcontacts are normally closed with the tag axle 106 in its normal levelor horizontal attitude as shown in FIGS. 28-30 and remain closed whenone of the tag axle wheels 110 (in the illustrated example theright-side wheel) encounters a depression 306 such as a recess orpothole with a depth less than 2.3-inches deep and for example onlyabout 1.7-inches deep resulting in a tag axle tilt angle of less than3.5-inches and in this example 2.5-degrees from being level orhorizontal as shown in FIGS. 31 and 32. And the proximity switches 286also remain closed in like manner when one of the tag axle wheels 110encounters a bump in a road less than 2.3-inches high causing the tagaxle to tilt less than 3.5-degrees.

But when one of the tag axle wheels 110 (in the illustrated example theright-side wheel) encounters a deeper recess 308 that is 2.3-inches deepthat causes the tag axle to tilt 3.5-degrees as shown in FIGS. 33 and 34or is deeper, the contacts in the proximity switch 286 on the oppositewheel side are then opened by the associated magnet 288 whereby the tagaxle 106 is then relieved of pressured down force and the tag axleservice brakes 114 are disabled as earlier described. And wherein afterthe affected tag axle wheel 110 is past such an encounter, the tag axle106 is returned by the tag axle gas springs 216 to its normal levelattitude and the opened proximity switch is restored to its normalclosed condition to reestablish the tag axle 106 in its normal activecondition with the tag axle fully pressured down and the tag axleservice brakes 114 enabled. And similarly, the pressured down force onthe tag axle 106 is relieved and the tag axle service brakes 114 aredisabled by the opening of one of the proximity switches 286 when one oftag axle wheels 110 encounters a bump in a road causing the tag axle totilt 3.5-degrees or more. Such as the bump 310 shown in the distance inFIG. 33 just ahead of the right-side wheel 110 whose height is the sameor greater than the depth of the recess 308 and would cause tilting ofthe tag axle in the opposite direction and thus opening of theright-side proximity switch 286 to effect relief of the pressured downforce on the tag axle and disabling of the tag axle wheel servicebrakes. And again with the tag axle active condition restored and thetag axle wheel service brakes enabled after the affected tag axle wheelis past such a bump. And whereby in either the case of a deep recess orpothole or a high bump, shock loading at the affected tag axle wheel isisolated from the truck frame with the relief of the pressured downforce on the tag axle.

However, it will be appreciated that such relief of the pressured downforce on the tag axle and the disabling of the tag axle brakes isdependent on the response time of the operating system and is thereforedependent on the speed of the truck and the extent of the recess orpothole or bump in the path of the affected tag axle wheel. For example,a tag axle wheel encounter with either a deep recess or pothole or ahigh bump causing the tag axle to tilt 3.5-degrees or more can be sobrief that there is not sufficient time for the operating system toeffect the relief of the down force on the tag axle and the disabling ofthe tag axle brakes. Whereby the normal operation of the tag axle andtag axle brakes is then not interrupted but which works to advantage innot having to restore the tag axle and tag axle brakes to normaloperation as result of such a brief encounter and in thereby allowingfor example the added braking by the tag axle brakes to remain availablein an also suddenly occurring vehicle braking situation.

Furthermore, in the event that either one of the tag axle gas springs216 or either one of the tag axle tires 112 is no longer able to performits intended function and as a result allows the tag axle 106 to tilt orswing 3.5-degrees or more, one of the proximity switches 286 willsimilarly be opened to effect the relieving of the pressured down forceon the tag axle and the disabling of the tag axle wheel service brakesby the opening of the Up Valves 236 and 238 and the closing of the TagAxle Brake Valve 132. And under such circumstances, the relief orrelease of the pressured down force on the tag axle and the disabling ofthe tag axle service brakes remain while the tag axle continues to trailthe truck but at a tilted angle of 3.5-degrees or more and with the tagaxle tires 112 still engaging the road but not pressured down by the tagaxle suspension system and then only supporting the dead weight of thetag axle assembly.

For example, this can occur when one of the tag axle gas springs 216collapses as shown in FIG. 35 and when one of the tag axle tires 112deflates as shown in FIG. 36. But in these circumstances, the relief ofthe pressured down force on the tag axle and the disabling of the tagaxle service brakes remain unlike in passing over a severe depression orbump as earlier described. In which case, the truck operator can leavethe tag axle deployed with the tag axle service brakes disabled fortraveling to a service site with the tires still engaging the road butnot pressured down by the tag axle suspension system 108 and then onlysupporting the dead weight of the tax axle assembly. Or the operator canraise the tag axle to its stored inactive condition for traveling to aservice site.

In the case of one of the tag axle gas springs 216 collapsing (forexample the left-side tag axle gas spring as shown in FIG. 35) andwherein such collapse allows the tag axle 106 to tilt 3.5-degrees asshown or more and which translates to 2.3-inches upward movement or moreat the left-side wheel and the same amount but downward at theright-side wheel, the pressured down force on the tag axle 106 isrelieved and the tag axle service brakes 114 are disabled with theresulting opening of the proximity switch 286 on the side opposite thecollapsed tag axle gas spring. But unlike an encounter with a severebump or depression that would only temporarily open one of the proximityswitches as previously described, the tag axle remains excessivelytilted with the one collapsed gas spring 216 but without the pressureddown force while the tires 112 of the tag axle wheels 110 remain incontact with the road but now only carrying or supporting the deadweight of the tag axle assembly and with the tag axle stabilized at thisangle by the other gas spring 216. And with the disabling of the tagaxle service brakes 114 then preventing any braking being applied to thetag axle wheels 110 while one of the tag axle gas springs is collapsed.

In the case of one of the tag axle tires 112 deflating (for example theright-side tag axle tire as shown in FIG. 36) allowing the tag axle 106to tilt 3.5-degrees as shown or more, the pressured down force on thetag axle 106 is relieved and the tag axle wheel service brakes 114 aredisabled with the opening of the proximity switch 286 on the sideopposite the deflated tire. And in this case, the tag axle gas spring216 on the side opposite the deflated tire on release of the pressureddown force on the tag axle acts to limit the tag axle tilt angle suchthat the tag axle wheel with the deflated tire is prevented fromcontacting the road and thereby being damaged while the truck continuesto be driven but then with the tag axle only supporting the dead weightof the tag axle assembly. And wherein the gas springs 216 so perform bylimiting the tag axle tilt angle to trip the proximity switches to anextent sufficiently less than the radial dimension of the tag axle tiresoutward their wheel and which in the exemplary embodiment is effected bythe proximity switches being tripped at the 3.5-degrees tag axle tiltangle. And wherein with both the release of the pressured down force onthe tag axle and disabling of the tag axle brakes, the deflated tire isnot subjected to other than the dead weight of the tag axle assembly andcould otherwise be significantly damaged if required to run flat withmore than this dead weight and could be damaged even with this deadweight if its wheel was braked.

Moreover, should power be lost to the relay 294 because of damage to theTag Axle Tilt Angle Sensors or their wiring, the tag axle will berelieved of the pressured down force and the tag axle service brakesdisabled. Thus allowing the vehicle operator to drive the truck to aservice site with the tag axle remaining deployed but no longer havingto help support the truck frame. Or the vehicle operator can establishthe tag axle in its stored inactive condition for travel to a servicesite under such circumstances.

Thus it will be appreciated that the tag axle suspension systemincluding the primary and secondary tag axle suspension providessignificant advantages, the relieving of the pressured down force on thetag axle under certain circumstances provides significant advantages,the disabling of the tag axle service brakes under certain circumstancesprovides significant advantages, and the tag axle operating systemprovides significant advantages in how it operates to effect the tagaxle force relief and the tag axle brake enabling and disabling. And inthe above exemplary embodiment, all their features are combined toprovide all their advantages. But they also have the attributes of beingseparable and distinct as well as being suitable to other types ofpayload-carrying motor vehicles employing a tag axle.

Another embodiment of the present invention is shown in FIG. 37 andcomprises a dump truck 312 like that in the previous embodiment buthaving a longer frame 314, a longer truck body 316, a cab 318 thatoverhangs the steer axle 20, and two additional pusher axles 24 havingwheels 36 with tires 42 and service brakes, and suspension systems 30.And wherein a service/storage compartment 320 now houses the engine,transmission and fuel tanks that are positioned between the cab 318 andtruck body 316 and wherein the fuel tanks are mounted inboard below theframe. And wherein the number of pusher axles now totals five which isthe maximum number possible allowed by the space available between thesteer axle tires 38 and the forward most drive axle tires 40 in thissignificantly stretched truck frame and truck body arrangement.

It will also be appreciated that having disclosed exemplary embodimentsof the invention, persons skilled in this art may arrive at variousversions or modified forms of the invention constituting otherembodiments and as adapted to other types of payload-carrying motorvehicles with or without a tailgate. And wherein for example other typesof tilt angle sensors for the tag axle may be employed such as forexample other types of suitable proximity switches and other kinds ofsuitable motion sensors. And within the prescription of preventing tagaxle wheel contact with a road surface in the event of a tag axle tiregoing flat, the allowed tilt angle may for example be increased withinthe available stroke of the gas springs beyond that in the exemplaryembodiments in order to allow larger tag axle wheel amplitude withoutrelieving the force on the tag axle and disabling the tag axle brakes.With such larger accompanying tag axle wheel amplitude without tag axleforce relief and brake disabling accomplished by simply adjusting thepositions of the tag axle tilt sensors relative to their magnets in thecase of magnetically operated proximity switches as employed in theexemplary embodiments. And therefore the scope of the invention isintended to be limited only by the scope of the appended claims.

1. A tag axle operating system for a tag axle having wheels with tires and air brakes wherein the tag axle is suspended from a motor vehicle and is raised and lowered by pivotal movement about a first axis by operation of parallel-arranged hydraulically-operated actuators and can also pivot about a second axis located equidistant from the tag axle wheels and laying in a plane at right angles to the first axis, said system comprising a closed gas circuit charged with a gas at a prescribed gas pressure, a hydraulic circuit adapted to deliver hydraulic fluid under pressure to the actuators to raise and establish the tag axle in an inactive condition and to lower and establish the tag axle in an active condition, said hydraulic circuit adapted when the tag axle is in said active condition to establish a prescribed hydraulic operating pressure opposing the gas pressure and a resulting force on the tag axle forcing the tires to bear against a road surface and the tag axle to accept a predetermined load, a brake valve adapted to allow air under pressure to be delivered to operate the air brakes while said prescribed hydraulic operating pressure is maintained and to prevent such delivery to thereby disable the air brakes when said prescribed hydraulic operating pressure is relieved, and said hydraulic circuit adapted while the tag axle is in said active condition to relieve said prescribed hydraulic operating pressure and thereby relieve the force on the tag axle and disable the air brakes when the tag axle experiences a predetermined tilt angle when pivoting about the second axis.
 2. A tag axle operating system as set forth in claim 1 wherein said hydraulic circuit includes a pair of up valves and a pair of down valves, one of said up valves adapted in an open condition to deliver hydraulic fluid under pressure to raise the tag axle and the other of said up valves adapted in an open condition to exhaust hydraulic fluid used to lower the tag axle, one of said down valves adapted in an open condition to deliver hydraulic fluid under pressure to lower the tag axle and the other of said down valves adapted in an open condition to exhaust hydraulic fluid used to raise the tag axle, and tilt sensor means adapted to effect the establishment of said up valves in their open condition while said down valves are in their open condition to thereby effect the relief of said prescribed hydraulic operating pressure.
 3. A tag axle operating system as set forth in claim 1 wherein the tag axle is also pivotal about a third axis parallel to the first axis and is toggled by pivotal movement about the third axis into a stored location by a hydraulically-operated toggle-linkage actuator, and said hydraulic circuit adapted to deliver hydraulic fluid under pressure to the toggle-linkage actuator to establish the tag axle in the stored location following raising of the tag axle and to deliver hydraulic fluid under pressure to establish the tag axle in the operating condition while the tag axle is being lowered.
 4. A tag axle operating system as set forth in claim 1 wherein said hydraulic circuit includes a dump valve adapted in a closed condition to allow the delivery of hydraulic fluid under pressure to raise and lower the tag axle and adapted in an open condition to limit the hydraulic pressure available to raise and lower the tag axle, pressure sensing means adapted to sense the hydraulic pressure lowering the tag axle and at said prescribed hydraulic operating pressure establish said dump valve in said open condition to thereby establish said prescribed hydraulic operating pressure, and a check valve adapted to maintain said prescribed hydraulic operating pressure while said dump valve is in said open condition.
 5. A tag axle operating system as set forth in claim 2 wherein said tilt sensor means comprises a pair of tilt sensors, one of said tilt sensors adapted to effect the establishment of said up valves in their open condition while said down valves are in their open condition when the tag axle experiences the predetermined tilt angle when pivoting in one direction about the second axis, and the other of said tilt sensors adapted to effect the establishment of said up valves in their open condition while said down valves are in their open condition when the tag axle experiences the predetermined tilt angle when pivoting in an opposite direction about the second axis.
 6. A tag axle operating system as set forth in claim 5 wherein said tilt sensors are magnetically operated sensors.
 7. A tag axle operating system for a tag axle having wheels with tires and air brakes wherein the tag axle is suspended from a motor vehicle and is raised and lowered by pivotal movement about a first axis by operation of parallel-arranged hydraulically-operated actuators and can also pivot about a second axis located equidistant from the tag axle wheels and laying in a plane at right angles to the first axis, said system comprising a closed gas circuit charged with a gas at a prescribed gas pressure, a hydraulic circuit including electrically-operated up valve means and down valve means, said up valve means adapted when supplied with electrical power to provide for delivery of hydraulic fluid under pressure to the actuators to raise and establish the tag axle in an inactive condition, said down valve means adapted when supplied with electrical power to provide for the delivery of hydraulic fluid under pressure to the actuators to lower and establish the tag axle in an active condition, said hydraulic circuit adapted when the tag axle is in said active condition to establish a prescribed hydraulic operating pressure opposing the gas pressure and a resulting force on the tag axle forcing the tires to bear against a road surface and the tag axle to accept a predetermined load, an electrically-operated brake valve adapted when supplied with electrical power to allow delivery of air under pressure to operate the air brakes and when without electrical power prevent such delivery to thereby disable the air brakes, pressure responsive switch means adapted to deliver power to said brake valve only while said prescribed hydraulic pressure is maintained, and tilt sensor switch means adapted while the tag axle in said active condition to effect delivery of electrical power to said up valve means while said down valves are receiving power to thereby relieve said prescribed hydraulic operating pressure and thereby relieve the force on the tag axle and disable the air brakes when the tag axle experiences a predetermined tilt angle when pivoting about the second axis.
 8. A tag axle operating system as set forth in claim 7 wherein said tilt sensor switch means comprise a pair of proximity switches wherein one of said switches is adapted to effect delivery of electrical power to said up valve means when the tag axle experiences said predetermined tilt angle when pivoting in one direction about the second axis and the other of said switches is adapted to effect delivery of electrical power to said up valve means when the tag axle experiences the predetermined tilt angle when pivoting in an opposite direction about the second axis.
 9. A tag axle operating system as set forth in claim 7 wherein said hydraulic circuit includes an electrically-operated dump valve adapted to open when supplied with electrical power and provide for the delivery of hydraulic fluid under pressure by said up valve means and said down valve means to raise and lower the tag axle and adapted to close when without electrical power and limit the hydraulic pressure available to raise and lower the tag axle, said pressure operated switch means adapted to deliver power to said dump valve while sensing the hydraulic pressure lowering the tag axle and at the prescribed hydraulic operating pressure interrupt electrical power to open said dump valve and thereby establish said prescribed hydraulic operating pressure and enable operation of the air brakes, and a check valve adapted to maintain said prescribed hydraulic operating pressure while said dump valve is open.
 10. A tag axle operating system as set forth in claim 8 further comprising an electrical relay adapted to be maintained in a condition by cooperative action of the proximity switches to prevent delivery of electrical power to the up valves when the tag axle is at an angle less than the prescribed tilt angle and is conditioned by the action of one of the proximity switches to deliver power to the up valves when the tag axle experiences the prescribed tilt angle.
 11. A tag axle operating system as set forth in claim 8 wherein said switches are magnetically operated proximity switches having a magnet that operates the switch and is stationary with respect to the tag axle. 